The presently disclosed embodiments relate to pneumatic sheet feeders.
In the process of electrophotographic reproduction, a light image of an original to be copied or printed is typically recorded in the form of a latent electrostatic image upon a photosensitive member, with a subsequent rendering of the latent image visible by the application of electroscopic marking particles, commonly referred to as toner. The visual toner image can be either fixed directly upon the photosensitive member or transferred from the member to another support medium or substrate, such as a sheet of plain paper. To render this toner image permanent, the image must be “fixed” or “fused” to the paper, generally by the application of heat and pressure.
With the advent of high speed xerography reproduction machines wherein copiers or printers can produce at a rate in excess of three thousand copies per hour, the sheet handling system must feed paper or other media through each process station in rapid succession in a reliable and dependable manner in order to utilize the full capabilities of the reproduction machine. The sheet handling systems must operate flawlessly to virtually eliminate the risk of damaging the recording sheets and generate minimum machine shutdowns due to misfeeds or multifeeds.
A high speed xerography reproduction machine typically includes a feeder assembly for feeding sheets to the image transfer portion of the machine. The feeder assembly may employ, for example, friction retard or vacuum belt corrugation feeder technology with air assist, or shuttle feeder technology. The feeder typically has a fixed set of operating parameters. These settings may be the best compromise for feeding most types of sheets, and, as a result, the sheet feeding capability is generally limited to the range that these parameters allow. While this approach may satisfy the needs of general use copying and printing, it limits the range of sheets that can be fed in the production environment where expanded range is needed. In response to this problem, feeder control systems have been developed which provide the users of high speed xerographic machines with the ability to adjust some of the feeder operating parameters to expand the range of sheets (from very light to extra heavy weight) that can be used with the machines.
Pneumatic sheet feeders use both vacuum pressure and positive pressure to separate and acquire a single sheet from a stack. The positive pressure is used to fluff the sheets to separate the top sheets in the stack. If the fluffer pressure is too high, multiple sheets can be sent at one time, causing a paper jam or the inclusion of blank sheets in a stack of printed material.
The optimal fluffer pressure changes as sheets of different weight are fed. A single sheet feeding apparatus typically is designed to accommodate sheets of varying weights. To avoid multifeeding of sheets, the fluffer must therefore have a blower speed that can be adjusted depending upon the weight of the sheets being fed.
The time required to adjust the fluffer or other device to the appropriate pressure when sheet weight is changed results in a delay in feeding. It would be useful to develop a system that has minimal time delays for adjusting pressure while ensuring that sheet feeding errors are prevented.